1. Field of the Invention
The present invention relates to a waveguide horn antenna array having a plurality of waveguide horn set in a feed waveguide with a fixed arrangement pattern and a radar device for performing target detection by using the antenna.
2. Description of the Related Art
In radar devices, etc., using the millimeter waveband, by utilizing the fact that transmission loss is less in waveguides than in planar circuits such as microstrip lines, etc., waveguide antenna arrays are used more than planar-circuit type antenna arrays.
Among related waveguide antenna arrays, as shown in Japanese Unexamined Patent Application Publication No. 10-32423, a connection waveguide is connected by T-branching in a perpendicular manner to one wall surface of a feed waveguide. Furthermore, as shown in Japanese Unexamined Patent Application Publication No. 2000-9822, the extending direction of a feed waveguide is perpendicular to the extending direction of a plurality of connection waveguides connected to horns. Correspondingly, one side wall of the feed waveguide is in contact with one side wall of the connection waveguide, and a coupling hole is formed in the wall contacting with the other wall.
However, in the related waveguide antenna arrays described in the above Japanese Unexamined Patent Application Publication No. 10-32423 and Japanese Unexamined Patent Application Publication No. 2000-9822, the degree of coupling between the feed waveguide and the connection waveguide is dependent on the opening area of the coupling hole formed in the plane surface portion where the waveguides are connected to each other. On the other hand, the shape of the feed waveguide and the connection waveguide is decided by a millimeter wave signal to be transmitted, the connection area between the feed waveguide and the connection waveguide is not large, the coupling hole is formed in the connection portion, and accordingly, the shape of the coupling hole is naturally limited. In this way, in the structure where the feed waveguide and the connection waveguide are coupled by forming a coupling hole on the connection surface, the adjustment range of the degree of coupling cannot be increased.
Furthermore, in the waveguide antenna array described in Japanese Unexamined Patent Application Publication No. 2000-9822, since many parts are required and the structure becomes complicated, it is difficult to form a waveguide antenna array of small size.